Amorphous Co@TiO2 heterojunctions: A high-performance and stable catalyst for the efficient degradation of sulfamethazine via peroxymonosulfate activation

Persulfate-based advanced oxidation processes (AOPs) cannot easily achieve the efficient degradation of persistent organic pollutants (POPs) with high stability. In this study, a simple in situ precipitation method was used to prepare an amorphous Co@TiO₂ heterojunction catalyst. The deposition of Co oxide on TiO₂, which is relatively nontoxic, efficiently activated peroxymonosulfate (PMS) to degrade sulfamethazine (SMT) and reduce the leaching of Co ions (0.915%). A catalytic system prepared using 0.3 g L^-1 Co@TiO₂ and 0.5 g L^-1 PMS could degrade SMT within 30 min with a degradation rate of 95.8%. Co@TiO₂ could activate PMS over a wide pH range (5.00-9.00) to efficiently degrade other antibiotics and dyes. Radical-capture experiments and electron paramagnetic resonance analysis suggested that SMT degradation occurs through a combination of the free radical and non-radical pathways, in which singlet ¹O₂ played a major role. Owing to the novelty of the proposed composite materials, the degradation path of SMT, which was determined through liquid chromatography-mass spectrometry, differed from that reported previously. This study provides not only an advanced and renewable catalyst for SMT degradation but also a feasible strategy for designing materials for AOPs.

Activation of peroxymonosulfate by a floating oxygen vacancies - CuFe2O4 photocatalyst under visible light for efficient degradation of sulfamethazine

In this study, expanded perlite supported oxygen vacancies-CuFe₂O₄ (OVs-CFEp) was synthesized via a simple method and utilized as floating catalyst to activate peroxymonosulfate (PMS) for the removal of sulfamethazine (SMT) under visible light irradiation. OVs-CFEp/Vis/PMS synergy presents much superior performance than that of OVs-CFEp/Vis system and OVs-CFEp/PMS system. PMS was efficiently activated by OVs-CFEp at a wide range of pH values, while the degrading rate of SMT was up to 95% in OVs-CFEp/Vis/PMS system. Oxygen vacancies and ·O₂^- accelerated the conversion of Fe(III)/Fe(II) and Cu(I)/Cu(II). The combination of the floating loader boosted light absorption capacity and sufficiently prevented metal ions leaching, which was all beneficial to enhance catalytic performance and recyclability. Besides, the reactive oxygen species were investigated systematically, proving that visible light and OVs-CFEp could activate PMS to produce ·SO₄^-, ·OH, O₂·^-, and ¹O₂ reactive species. Furthermore, based on intermediates identification and Density Functional Theory (DFT) calculation, three types and seven main degradation pathways involving cleavage of bond, SMT molecular rearrangement, and hydroxylation reaction were proposed. So this high photo-absorbing catalyst coupling with advanced oxidation progress was promising for extensive environmental remediation.

Modeling anaerobic digestion metabolic pathways for antibiotic-contaminated wastewater treatment

Anaerobic digestion has been used to treat antibiotic-contaminated wastewaters. However, it is not always effective, since biodegradation is the main removal mechanism and depends on the compound chemical characteristics and on how microbial metabolic pathways are affected by the reactor operational conditions and hydrodynamic characteristics. The aim of this study was to develop a mathematical model to describe 16 metabolic pathways of an anaerobic process treating sulfamethazine-contaminated wastewater. Contois kinetics and a useful reaction volume term were used to represent the biomass concentration impact on bed porosity in a N continuously stirred tank modeling approach. Two sulfamethazine removal hypotheses were evaluated: an apparent enzymatic reaction and a cometabolic degradation. Additionally, long-term modeling was developed to describe how the operational conditions affected the performance of the process. The best degradation correlations were associated with the consumption of carbohydrates, proteins and it was inversely related to acetic acid production during acidogenesis.

Distorted polymeric carbon nitride via carriers transfer bridges with superior photocatalytic activity for organic pollutants oxidation and hydrogen production under visible light

Polymeric carbon nitride (PCN) has become the most promising metal-free photocatalysts but its activity is low. Molecule doping of PCN has been proved to be an effective strategy to achieve high photocatalytic performance. Herein, we report a bottom-up method to synthesize modified PCN, which includes 2,5-dibromopyrazine doping, thermal-induced exfoliation and condensation/polymerization. The incorporation of electron-deficiency 2,5-dibromopyrazine into the PCN framework can effectively tune the electronic structures and improve the charge-carrier separation. In addition, the incorporation of 2,5-dibromopyrazine induced significant structural changes from planar symmetric to distortion. The optimized pyrazine doped PCN showed a reaction rate enhancement of 4-fold for the degradation of sulfamethazine compared to that of conventional urea-based PCN. Further reactive species and degradation intermediate detection studies, indicated that O₂^- was generated during the photocatalytic process, which could lead to the decomposition, and finally mineralization of sulfamethazine. 2,5-Dibromopyrazine doped PCN also leads to a 6.3-fold improvement in H₂ generation with the visible light. Especially, phytotoxicity experiments showed that the toxicity of sulfamethazine after degradation is greatly reduced, and the as-prepared photocatalyst is environmentally friendly.

Visible-light-driven photocatalytic degradation of sulfamethazine by surface engineering of carbon nitride：Properties, degradation pathway and mechanisms

Polymeric carbon nitride semiconductor has been explored as emerging metal-free photocatalyst for solving the energy shortage and environmental issues. However, the efficiency of carbon nitride is still not satisfying. Herein, a facile copolymerization between L-cysteine and dicyandiamide has been applied to forming the modified carbon nitride photocatalysts. The photocatalytic performance was evaluated through degrading sulfamethazine under visible light illumination. The ameliorative structure and tuned energy band result in visible-light adsorption enhancement. In addition, nitrogen vacancies offer more sites to adsorbing molecular oxygen, thereby facilitating the transfer of electrons from carbon nitride to the surface adsorbed oxygen. As a result, the degradation rate of optimized modified carbon nitride sample for sulfamethazine was 0.1062 min^-1, which was almost 12 times than that of carbon nitride (0.0086 min^-1). Superoxide radicals and holes were mainly responsible for the sulfamethazine photodegradation by modified carbon nitride. Two reaction intermediates/products were observed and identified by high performance liquid chromatography-mass spectrometer, and a possible reaction pathway was proposed. This study provides new insights into the design of highly efficient photocatalyst for other organic pollutants degradation.